Inhibitor of apoptosis proteins (IAPs) are a family of antiapoptotic proteins that suppress apoptosis by binding to and inhibiting caspases 3, 7 and/or 9. Members of IAP family are characterized by a novel baculoviral IAP repeat (BIR) domain (approximate 70 amino acids) in which a conserved cysteine and histidine residues (Cx2Cx6Wx3Dx5Hx6C) represents a novel zinc-binding fold. However, not all proteins with BIR domain qualify to be an IAP family member. The ability to suppress apoptosis is required as well. So far, eight members of human IAP family have been identified, which are divided into three classes, including class I (XIAP, cIAP1, cIAP2, ILP2 and MLIAP), class II (NAIP) and class III (SURVIVIN and BRUCE).